您可以创建这个半渐变使用xml 图层列表，将顶部和底部的乐队组合成一个文件每个乐队都是一个xml形状。

有关详细的教程，请参阅SO上的以前的答案：多梯度形状。

I want to create gradient background as in the picture. but it can't because of the centerColore was spread out to cover bottom and top.

How can I make a background like picture below? or How can I make small ceterColor that not spread out? did you have any idea?

This is the background that i want.

This is the background that I made.

This is code in xml of background button above

<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle" >
    <gradient 
        android:startColor="#6586F0"
        android:centerColor="#D6D6D6"
        android:endColor="#4B6CD6"
        android:angle="90"/>
    <corners 
        android:radius="0dp"/>


</shape>

You can create this 'half-gradient' look by using an xml Layer-List to combine the top and bottom 'bands' into one file. Each band is an xml shape.

See this previous answer on SO for a detailed tutorial: Multi-gradient shapes.